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Date:      Fri, 11 Apr 2008 08:34:29 -0400 (EDT)
From:      Andrew Gallatin <gallatin@cs.duke.edu>
To:        gnn@freebsd.org
Cc:        current@freebsd.org
Subject:   Re: TSC Timecounter and multi-core/SMP
Message-ID:  <18431.23276.913397.188219@grasshopper.cs.duke.edu>
In-Reply-To: <m2d4oy8n30.wl%gnn@neville-neil.com>
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gnn@freebsd.org writes:
 > Howdy,
 > 
 > Is the TSC timecounter synchronized across multiple cores and/or
 > processors?  A quick search seems to indicate it's not but I'd like to
 > find a definitive reference on the TSC.

There is a great comment in the OpenSolaris source code talking about
TSCs and their behavior on SMP systems.  See
http://cvs.opensolaris.org/source/xref/onnv/onnv-gate/usr/src/uts/i86pc/os/timestamp.c

FWIW, solaris manages to keep track of unsynchronized TSCs, and use
unsynchronized TSC timecounters for timekeeping on SMP systems.  It
would be nice if FreeBSD could do the same.

Drew
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